1. Field of the Invention
This invention relates to a multiple port optical fiber switch for providing for the exchange redirection of one common optical path with one of a plurality of other optical paths. It further relates to a prism for exchanging the optical paths of two initially parallel beams by means of four refractions at their entry and exit points and two internal reflections per beam within the prism. Accordingly, it is a general object of this invention to provide new and improved switches and prisms of such character.
2. Introduction
There are a variety of applications, in fiber optics communications systems, for switches that are capable of reconnecting a set of n input lines to n output lines. A particular type of such a switch is required in a system in which several laser transmitters are feeding data signals into an equal number of fiber circuits and one additional laser transmitter is operating with a test signal in a standby mode ready to serve as a replacement if any one active transmitter should fail. Such a complex switching function could be implemented by interconnecting a network of simpler 2.times.2 matrix array switches, but this would result in the passage of optical signals successively through several switching devices and could result in excessive cumulative signal loss.
3. Description of the Prior Art
As a means of complying with the duty of disclosure set forth in 37 CFR 1.56, the following listing of publications may be considered to be pertinent. A concise explanation of the relevance of each of the listed items is indicated by the references set forth in the following paragraphs with the various cited items being indicated by superscript reference numerals. This disclosure statement shall not be construed as a representation that a search has been made or that no other material information as defined in 37 CFR 56(a) exists.
1. P. G. Hale and R. Kompfner, "Mechanical Optical Fibre Switch," Elec. Lett. 12(15), 388 (1976). PA1 2. M. Johnson and R. Ulrich, "Fiber-Optic Relay," Appl. Phys. Lett. 31(10), 675-676 (1977). PA1 3. M. Stockman, G. Winzer, and E. Grassl, "Rigid Reed-Type Routing Switch for Multimode Optical Fibers," Fiber and Integ. Opt. 3(2-3), 237-251 (1980). PA1 4. T. Ebato, T. Kajiwara, and S. Kobayashi, "Mechanical Fibre Optic Switching Using P.V.D.F. Bimorph," Elec. Lett. 16(22), 829-830 (1980). PA1 5. A. Carenco and L. Menigaux, "InP Electro-Optic Directional Coupler," Appl. Phys. Lett. 40(8), 653-655 (1982). PA1 6. M. Kondo, Y. Ohta, M. Fujiwara, and M. Sakaguchi, "Integrated Optical Switch Matrix for Single Mode Fiber Networks," IEEE J. of Quant. Elec. QE-18(10), 1759-1765 (1982). PA1 7. M. Haruna and J. Koyama, "Thermooptic Deflection and Switching in Glass," Appl. Opt. 21(19), 3461-3465 (1982). PA1 8. Y. Fujii, J. Minowa, T. Aoyama, and K. Doi, "Low Loss 4.times.4 Optical Matrix Switch for Fiber-Optic Communications," Elec. Lett. 15(14), 427-428 (1979). PA1 9. J. Minowa, Y. Fujii, Y. Nagata, T. Aoyama, and K. Doi, "Nonblocking 8.times.8 Optical Matrix Switch for Fibre-Optic Communications," Elec. Lett. 16(11), 422-423 (1980). PA1 10. R. Watanabe and K. Asatani, "1.times.2 Optical Switch Using New Type of Pentagonal Prism," Elec. Lett. 16(7), 257-259 (1980).
Various optical fiber switches have been devised in the past. Some switches.sup.1-4 electromechanically recouple the end of one fiber alternatively to the ends of two other fibers. These have been most successful with multimode fibers where the alignment is not as critical as with single mode fibers. In others.sup.5-7, the light from the fibers is coupled into a planar waveguide system in thin film devices where its path is controlled by means of an electro-optic or thermo-optic effect. Most of these switches require the light from the fiber to be polarized for proper operation; however, with the exception of thermo-optic devices, they operate at very high speeds.
In another class of switches for optical fibers, light can be manipulated in free space after emerging from the fiber and being focused into a parallel beam by a lens connector device, such as disclosed and claimed in U.S. Pat. No 4,421,383, issued Dec. 20, 1983, to Carlsen, and assigned to the common assignee of this specification. Such a connector can include, in one small part, a conical fiber alignment port and a lens surface to focus the wave into a parallel beam, such as disclosed in pending U.S. patent application No. 454,943, "Optical Fiber Centering Device", filed Jan. 3, 1983, by Paul Melman and W. John Carlsen, and assigned to the common assignee of this specification, a continuation-in-part of U.S. patent application Ser. No. 223,192, filed Jan. 7, 1981. Use of such connectors on opposite sides of a free space optical switch greatly relaxes the lateral alignment requirements of the assembly.
Several such free-space beam switches using electromechanically driven prisms have been described. In one.sup.8, two parallel input beams switch output positions when a rhombic glass prism is inserted into their paths so as to cause them to cross each other. A pair of electromagnets are required to move the prism into and out of the beam switching position. In another.sup.9, a square array of pentagonal prisms is used to implement an 8.times.8 switch matrix. In both cases, a linear prism drive that maintains accurate orientational alignment is required. In still another.sup.10, a pentagonal prism is described that makes use of total internal reflection while giving a fixed 90.degree. beam deviation.